iron eagel

I am in the process of designing a airfoil shaped horizontal stabilizer to replace the slab design on an Sig Somethin Extra I am building. Here is the questions I have:
From an aerodynamic standpoint is it ok to go from say 3/8 thick at the root (thickest part of the airfoil) and taper that to 1/8 or so at the tip, to reduce drag. The theory I am working with here is the sheathing at an angle to the tip and root should add a bit of stiffness to the stabilizer and the reduced frontal area should reduce the drag.
The second part of my question is, will this reduce the effectiveness of the elevator where it is essentially a high aspect ratio wing given the overall deign of the stabilizer/elevator combo?
I am also considering treating the vertical stabilizer and rudder in the same manner, am I going to cause myself any problems by doing this?

pimmnz

There will be no aerodynamic differences that you will notice while flying by using a symmetric (zero camber) section on the tail surfaces. The tailplane/elevator is actually just a variable camber airfoil anyway, not two 'wings' hinged together. The fin/rudder is essentially the same. No doubt there will be plenty of other opinions, but the proof of the pudding etc. is when you fly the thing anyway.
Evan, WB #12.

BMatthews

Look again at the wing on the Sumthin' Extra. Now tell me again why you're worried about reducing drag in an airfoiled stabilizer?

As for thick vs thin..... Normally a thicker section tends to stall at a higher angle of attack than a thin one. But with stabilizers and fins it's a different story since they are variable camber sections due to the fixed and moving portions. So the rules the wing follows don't totally apply. The variable camber means that a thicker section isn't as important. This is why a lot of classic planes can happlily get away with flat tail airfoils.

All that being said it's possible that the airfoil nose will help keep the air more attached up to a point but given the deflection angles used in a not of 3D airplanes avoiding a stall is near impossible. But just because the tail sections are stalled in the rear half doesn't mean the tails stop lifting. They still do that very well.

iron eagel

Bruce and Evan,
Thanks a lot for taking the time to reply!
I know given the main wing I am not going to gain all that much in performance given the time and effort to build airfoil shape tail section. I was just concerned that by using the taper from the root to the tail I would increase the span-wise flow and mess up the effectiveness of the rudder and elevator.
And where my knowledge is limited I had no idea that it is considered as a variable camber airfoil to start with.

As far as going through all the pain and anguish to build such component into this plane is mostly for practice to refine my building techniques when I get into airplanes where it will really matter, such as large scale or high speeds.

Sorry for pestering you with questions but as I sit sanding balsa for skins and work out the design of the tail feathers I would like to use, these questions keep popping into my mind, and I feel the need to get some input from those with more knowledge than myself. I have formal training in engineering (electrical, not mechanical or aerodynamics) and not knowing all the ins and outs to aerodynamics and structural engineering I keep coming up with these questions during the course of my build.

pimmnz

Iron Eagle,
There are no stupid questions, but you find that you will get some really 'interesting' answers...!
Evan.

da Rock

iron eagle,
While you're mulling over the astute answers, remember that the beauty of our hobby is that we always get 100% truthful answers from the model. And take comfort that seldom does anything we try cause major changes.

The really good benefit from built up stabs is strength. And often there is no significant increase in weight. win win The really fun return on the time and effort is that YOU will see just how little increase in weight you got and will be able to tell newbies your findings..... and then join the masses that THEY REFUSE TO BELIEVE.

As for the thickness taper causing problems. No real problems with a tail.

Thickness tapers by themselves actually don't do much. But if they are not in proportion to the change in chord from root to tip, they cause a change in the airfoil from root to tip. That might matter in a wing. And it might be a good thing.

Control Line precision aerobatics guys very often built wings with tapering planform. And usually changed the thickness from root to tip. And did it sometimes to reduce the tip stall potential. They tapered the thickness LESS than they tapered the chord and wound up with a wing that still tapered down in both thickness and chord. But by having a slightly "thicker" airfoil at the tip, got a later stalling tip.

Fun thing about all that high tech description and discussion? Nobody can really prove you wrong. And most judges couldn't even follow the ideas, so were suitably impressed. Which was the point of talking about it in the first place. Good thing was that it actually did seem to work. And if it seems to work for you, it is working for you.

iron eagel

Da Rock,
Thanks again for your thoughts...
You know that keeping the weight down is one of my primary considerations as I progress with this build. The next and primary reason for these modifications is strength of the structure so I can eliminate the external brace wires and the weight of their entire assembly. I weighed the balsa components used in the construction of the stock tail feathers (Horiz. and Vert. Stabs., Rudder and elevator and found that they weigh a total of 2 Oz alone. I will also weigh the guy wires, and mounting hardware and add that to the total and see if my built up system will less than that total if possible, and I would feel like I made some progress.

I know at the Rn's we work at drag reduction is looked at as a "black art" of some sort and any real gains are probably to small to really notice or even measure without a lot of fancy instrumentation....


I like a nice "clean" airframe on an aircraft from the looks, as much as any performance enhancement gained.
Not to mention ,it is neat that we can experiment with these types of things, just because we can.

HighPlains

My Feedback: (1)

Sounds like you are looking to put a expensive English riding saddle on a pig and expecting to ride a throughbred. Not going to happen. The result of any drag reduction would be buried in the wake of the rest of the airframe. On a design like that, weight reduction would be noticed, little else.

iron eagel

HighPlains you are indeed correct...

I am just trying to spruce the pig up a bit, while trying to hone my design and building skills a bit, and hopefully gain some more knowledge in the process....
Hopefully the weigh reductions thus, far along with the reduced weight in the tail ,will offset the weight of the wing fairings I am adding to blend the wing into the fuselage. The intent with the fairings is to help reduce the turbulent airflow along the rest of the airframe.
In the end how will it perform, probably a lot like an SE.

rmh

forget the streamlining
look at the wing/stab/elevator rudder fin-- from a structural point of view
If yo u make the lightest structure which will still be strong enough- you have done your job correctly.
flat , rounded a little , who cares .
It is actually getting structure correct at the lowest weight ,that really counts.

Don't believe this ?
OK
turn back the pages of time -to the first half of the 20th century - look at the evolution of tail groups
Typically the air pressure on the elevator tends to deflect the stabilizer - so take care of twisting loads
bending loads should be obvious if you have some basic engineering.
stabs need to be STIFF-- elevators - not as stiff .

da Rock

The beauty of our hobby is that we can do whatever we want. For whatever reason we wish.

And then when our latest enhancement flies, it proves us right.

Hey, it IS faster, isn't it. Watch that sucker go. It's gotta be 5 maybe 10mph faster than it would be otherwise, RIGHT!

So if you like the streamlining, do it. It WILL make a better model for you. And you can prove it. Or not. But they can't prove otherwise. And you both won. You both got what you wanted. A model that suits you.

Does everything we do make a difference? Yeah, to us.

The Internet Killer

Now there was a picture I could have done without seeing.

Last time I bought an english saddle the pig rode on it!! LOL



Sorry, I must have issuses.

iron eagel

It seems the only issue you may have is with the pigs...
LOL

Anyhow thanks for the input guys now time to get back to the build. I listed it as: Yet another Something Extra build in the kit forum, but it should have been titled more along the lines of a bash rather than a build, perhaps...

Anyhow, as far as the modification since it was my intent to max out a Sig SE since I am building a new stab and vertical fin assembly anyhow I wondered if I could enhance it, without causing other issues with the flight handling of the plane and perhaps gain some small amount of performance out of the basic design.

Thanks again everyone!
Regards,
Paul

iron eagel

Dick,
Your right getting it as light, and strong as possible has to be the number one goal. That was my thought about tapering the stab and alike as it travels out toward the tip. Since I am using a stressed skin design my thought was that that shoul help reduce the flex in the assembly where the skins would be at an angle to the root and span.

The original Balsa components for the stab,fin elevator and rudder is a bit over two ounces, I think it is possible to reduce that by at least 25% ( and that does not even include the weight of the wire braces and all of it components perhaps I should factor them in as well). While that may not be all that much I think that every gram you can take off of the wing loading will enhance the performance. And since your dealing with the moment of the aircraft every gram you can take out of the weight of the tail has a much larger effect than it has up forward.

rmh

Yes a double taper or a cone or a ellipse etc', is highly desireable -and a stressed skin stab is the strongest -
I spent years designing models for competition flying- pattern/TOC/IMAC etc...
Most of the designs were far lighter than contemporary types -because THIS aspect of the design means far more than trying to figure what "airfoil" meant the most
basically -we found thru experience -in the sizes we work with - weight is 1,2 and three in the list of importance to getting best performance.
It follows then -that structural knowledge is the most important part of getting the model right the strongest lightest design is the best .
every time.
Try this:
If the model is light enough -the airfoil is meaningless
Once you understand this - you are on th track to best performance.

iron eagel

Dick thanks for sharing you knowledge!

Weight is the first three, sounds like the first three rules in flying...

Fly the plane!


LOl

Paul

BMatthews

Simply put but oh so true.

For a study in how to build light if you ever get a chance to look at the plans for Al Rabe's very scale like control line stunt models I guarantee that you'll go out and jump on your own models in disgust as few of us are worthy in the light of such a builder.

OK, I'm exagerating of course but I can promise you that a 1/2 hour looking at the plans and reading the articles would be time well spent.

I keep writing around here in a tongue in cheek manner about you we should design to include a lot of air in our designs. It's not just a joke. And folks like Rabe did just that while still making drop dead gorgeous model designs.

rmh

Rabe really did great work -no doubt about it
He made scale like models which wre fully competitive in the ukie stunt arena
In today's market --the Chinese are doing some exceptional work --based on costruction methods we only dreamed of for years
cutting with a laser allows for ANY shape desired -replete with interlocking pieces which do not rely on glue.
Some of these guys are amazing.
having started -like many, with a saw and a knife and crummy "balsa which had grain going in all directions - I graduated to selecting woods which had grain that could be used to increase strength
Now the laser techniques allow use of thin very light cheap plywood cut as noted, however the design dictates.
Also foamed plastics of all types can be inclued to dampen resonances etc..
I am in hog's heaven now , using some of these techniques .
My next effort, is in doing competitive electric designs which work with the new A123 bateries
These things offer cheap reliable power with little risk .

the absence of vibration allows lighter structure than when using engines .
Scale models which once were simply grossly overweight can be done at half the wing loading .
The old excuse "Warbirds have to be heavy to be scale like " can be kicked aside.

iron eagel

There is a CL scale gut in my club by the name of Jack Petrolia (sp) from Marshfield that has a B24 that has to be seen to believed, A Pitts also that makes you wish you could sit in it.

My thoughts are why not upgrade the aerodynamics if you can while building it lighter.
I got the kit as a gift and just decided if I was going to build it why not try and see what I could do with it and make it lighter if possible. I will have to look at Al's models that name sounds familiar but I can't recall why (must be age related). I have seen models and builders one in particular who has the airfield models website, which after seeing his building I threw out a wing I had finished for my Cub. The second one I built was the same six foot span and ten inch cord and came out at 12 ounces sheathed and glassed, better than 10 ounces lighter than my first.
What I am trying to say is keeping in mind that I feel that weight of the airframe is an important aerodynamic consideration, if you can use enhanced materials to give you the chance to optimize the aerodynamic shape as well why not incorporate that as well?

But I do not have the actual working knowledge or experience that you guys have.

Lots of air in the design indeed, where can I get some helium...
LOL

Gremlin Castle

My Feedback: (14)

Here is a fair example of light building. It is my scaled ups and stretched KenHi Panther. 84" foam core wing

And the remainder is balsa. The airfoil for all surfaces is the old NACA 0015. Total weight 17 lbs with a Moki 1.8 for power. Flys like a pattern plane that is lazy in the rolls and lands like a Big Stick.

iron eagel

Oh yes the new electronics and batteries have throw a whole new slant on the warbird side! I have a top flite P39 that might get retracts and all driven by a brushless, been thinking about that ever since I volted my wifes LT-40 ( has a pair of A123's in series driving a Axi 4120/18) that weighs in at the same weight loaded as a glow LT-40 dry.

iron eagel

Nice airplane!

da Rock

Oh jeez..... LOSE the wire braces idea. It is a really silly idea when you consider how strong tails can be made on our models with just a very slight consideration of structure and materials.

I think it still around in the ARFs because they take almost no notice of materials.

It's actually diametrically opposed ideas to be considering one technique to streamline and strengthen, yet retain wire bracing.

If for any reason you feel the urge to wire brace anything, simply use sticks. Spruce is dependable and light and can be generally airfoiled. The glue to attach it is much lighter and simpler than the ridiculous hardware used with wire. The sticks can be TEN times the size of the wire and be LESS drag. Ten times.....

No lie. Wire braces on a model airplane are just plain bad.

rmh

Here is a trick I discovered -- use the old K&S streamline amuminum tubing - this stuff is extremely light and twist resistant - IMPORTANT!! This means that if it is properly attached - it reduces dramatically any possible twist in the flying surface. Don't believe it ? try it. the piece I used (36" ) is 1/2 " size --which I used on the scale Buckers I did for 1990 TOC models as LG brace covers
anyway -on this 16 oz (all up inc batts ) flat foamie which uses 4, A123 VPX cells - the wings are almost totally twist proof- the tubing is 31 grams for this size and they have smaller ones too which are perfect for tail bracing -just flatten the ends
The cross section makes em more rigid than any shape I have tried. far better than CF dowels or tubes.
This funny looking flat foam model, has a fuselage with same lateral area as the wing area .
The result makes for a really interesting aerobatic setup; You can do "flat" turns as fast -and with no apparant skid --as a banked turn.
So knife edge flying and maneuvering is much the same a s level flight . The other trick--I found--balancing the fuselage vertically- by placing the batteries above the wing. This improves rolls and knife edge flight .
I have adopted tricks I larnt from the funny fla tfoam models --to my big gassers - ( balance - power to weight - Low wing loading , the models really do fly better - -not as agile as the flat foam but better than they were before I started adopting learned techiniques from the flat foam stuff.

Of course the bigge was the "airfoil"- and importance of "shape".
I found that the lightest thinnest wing which was strong enough - was the best -- Look at Que Ques Biplnane flown to win the last F3A aerobatics - those airfoils must be only 7-8 %
That contest places a premium of acccurate smooth flying.
get the qeight down an you can reduce the airfoil thickness -and ofcourse the bipe configurationis a better beam load setup. (but a PTA to do -trust me on that one.

iron eagel

Da

Don't you recall that from the start the wire braces have not been part of my plan, they were included with the kit. I only mentioned them because I am going to lose them, I have not bothered to weigh them, but I can use that weight to add to the stock structure to see if I can actually reduce the weight from the stock setup. I am not going to go through all the effort of a build up stabilizer and elevator to stick those braces back on it.

Edited to add:

While laying out the new components for this assembly I came up with yet more questions.
Manny others have modified this airplane by adding both area and larger throws to the elevator and rudder to male them more effective. A lot have used counterbalances to the control surfaces as well.

Doesn’t the increase in span from the addition of counterbalances reduce things like roll response?

By adding more rudder surface up higher from the central axis via the counterbalance method , cause reverse roll coupling?

Isn’t it far better to increase the cord of the control surface closer to the central axis of the plane and pay the price of the higher drag that will cause rather than cause control coupling issues?

When you increase the cord you shift the MAC reward also does that not make the surfaces more effective because you are extending the moment arm?

One final question if I can reduce the mass of the components used in the tail surface construction will that not in itself make the control response better?